García-Alcántara C, Varea C
Universidad Nacional Atónoma de México, Apartado Postal 20-364, 01000 México D.R., Mexico.
Phys Rev E Stat Nonlin Soft Matter Phys. 2006 Sep;74(3 Pt 1):031603. doi: 10.1103/PhysRevE.74.031603. Epub 2006 Sep 14.
We study the wetting behavior on spherical walls by ternary mixtures of oil, water, and an amphiphile. We use the Ginzburg-Landau free energy with a single order parameter and find that there are different stable structures of the interface and that a quasiwetting transition is the mechanism involved in the transition among them. We calculate these wetting transitions for two sets of parameters in the bulk free energy which are known to show microemulsion behavior. The surface transitions are thin-thick first-order transitions (continuous transitions are absent), and the phase diagram in surface parameter space is constructed. For the first set of bulk parameters water, oil, and a microemulsion coexist, and we study the first-order transition where the oil phase wets the wall-microemulsion interface and its behavior as the radius of the wall becomes large. Therefore, we recover the known wetting transitions on a planar wall. In the second set of bulk parameters only water and oil coexist, and for some sizes of the solid wall, the oil phase wets the wall-water interface, and the phase behavior is extremely rich. We obtain a coexistence of four surface phases or two triple points followed by three lines of first-order transitions which end at three critical points depending on the radius of the surface. When there are micellar metastable solutions in bulk, the behavior of the thickness of the wetting layer of the oil phase as the radius of the spherical wall gets larger is nonmonotonic. We associate this behavior with the intrinsic micelle structure due to the spontaneous curvature of the model.
我们研究了油、水和两亲分子的三元混合物在球形壁上的润湿行为。我们使用具有单个序参量的金兹堡 - 朗道自由能，发现界面存在不同的稳定结构，并且准润湿转变是它们之间转变所涉及的机制。我们针对已知表现出微乳液行为的两组体自由能参数计算了这些润湿转变。表面转变是薄 - 厚一阶转变（不存在连续转变），并构建了表面参数空间中的相图。对于第一组体参数，水、油和微乳液共存，我们研究油相润湿壁 - 微乳液界面的一阶转变及其在壁半径变大时的行为。因此，我们恢复了平面壁上已知的润湿转变。在第二组体参数中，仅水和油共存，对于某些尺寸的固体壁，油相润湿壁 - 水界面，并且相行为极其丰富。我们得到四个表面相的共存或两个三相点，随后是三条一阶转变线，它们根据表面半径在三个临界点处结束。当体相中存在胶束亚稳溶液时，随着球形壁半径增大，油相润湿层厚度的行为是非单调的。我们将这种行为与由于模型的自发曲率导致的固有胶束结构联系起来。
